Over the last several decades, the development of novel butyl-based elastomers has been limited by the complexity of the methyl chloride (MeCl) slurry process. The current butyl process demands high purity feeds and a diluent (e.g., MeCl), as well as the use of extremely low temperatures (less than −90° C.). The polymerization is very rapid (close to diffusion control) and utilizes a Lewis acid initiator complex with either water or protic activator, further complicating the catalyst makeup and dosing of the reactors. Fouling of the reactors is also a problem in such a slurry process, resulting in reduced production rates caused by the frequent cleaning of the reactors. These factors make the current synthesis of new butyl polymers both costly and unforgiving.
Additionally, it is the extremely high rate of polymerization of isobutene that limits control of the polymerization process and polymer structure. The polymer precipitates from the commercially used diluent, methyl chloride. This prevents any further manipulation of the molecular structure. Very few co-monomers can be incorporated along with isobutylene, and in relatively low concentration as they typically cause rate depression, chain transfer and, in the case of dienes, branching and cyclization. In addition, all co-monomers increase the glass transition temperature (Tg), resulting in less desirable low temperature properties.
The present butyl process is 65 year old technology, and the previously mentioned limitations are a few of the main reasons for the development and commercialization of few new grades of butyl-based elastomers during the past 60 years. Furthermore, all of the new butyl-based elastomers, with the exception of star branched regular butyl, are manufactured by post-polymerization modification. This is typically carried out by dissolving the already precipitated base polymer in a hydrocarbon solvent and, following modification, isolating the polymer again via steam coagulation for finishing. Given this process, the production of these new butyl-based elastomers requires a significant amount of energy, and thus production thereof is very inefficient and costly.
Additionally, butyl-type (polyisobutylene-based) polymers find a wide range of uses in such areas as biomedical applications (e.g., stents and implants), tire applications (e.g., innerliners), food-related packaging applications, pharmaceutical closures and in various sealant applications.
As such, there is a need in the art for a process that permits the production of butyl-type polymers having controlled architecture, molecular weight, molecular distribution, branching, co-monomer distribution, and/or co-monomer sequencing, that is accomplished by independent control of the polymerization and initiation steps, as well as control of the overall polymerization rate.